var banner = new Array();

    banner.push('http://img189.imageshack.us/img189/5868/bannireforum1s.png');
    banner.push('http://img696.imageshack.us/img696/7566/bannireforum.png');
    banner.push('http://img827.imageshack.us/img827/3374/bannire3e.png');
    banner.push('http://img692.imageshack.us/img692/2179/bannireetcadre.png');
    document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];